170 Reviews—Dr. H. B. Guppy’s Geology of Solomon Islands. 
large additions from the shells and skeletons of pelagic organisms, 
as well as from those of animals living at the bottom. Three prin- 
cipal varieties are indicated in this group, which includes the 
majority of the so-called coral limestones found in the Solomon 
Islands. The non-calcareous matter, which is small in amount, con- 
sists of the common volcanic minerals, and a few glassy fragments, 
etc. The chalky coral limestones constitute a section of this group ; 
and the consolidated calcareous ooze of the channels, which forms 
compact fawn-coloured limestones of homogeneous texture, also is 
referred to this group. 
The third group comprises a still greater variety of rocks, corre- 
sponding in composition to the voleanic muds and pteropod oozes of 
the “Challenger.” These are composed of the débris of volcanic rocks 
mixed with the shells of Foraminifera, Molluscs and many other 
calcareous organisms. Judging from the Foraminifera they may be 
regarded as of Post-Tertiary age. 
The fourth group comprises the foraminiferal limestones, which are 
grey or yellowish-brown in colour, hard and compact in texture, and 
are chiefly made up of the tests of pelagic and bottom-living Foram- 
inifers. They usually contain from 70 to 85 per cent. of carbonate 
of lime, and may be described as the consolidated foraminiferous 
oozes of the “Challenger” and other expeditions. An interesting 
description of a Rhynchonella-limestone and some valuable remarks 
relative to the beach sand-rock, which is generally regarded as in 
some way connected with the formation of oolite, follow, and then 
comes a detailed description of the several calcareous islands. 
Dr. Guppy’s descriptions. of the calcareous formations of these 
islands afford, probably, the most complete account we have yet 
received of the role played by the deposits of the deep ocean in the 
formation of rock-masses; and, at the same time, it is difficult to 
conceive anything more interesting to geologists, who, if the charter 
of the Geological Society be accepted literally, are supposed to be 
desirous of investigating the mineral structure of the earth. This 
portion of the work is also, in the main free from controversial 
matter. 
It would, however, have been impossible for Dr. Guppy to have 
ignored the question of the mode of formation of coral reefs, when 
engaged in the general physical investigation of the Solomon Islands. 
His conclusions on this point may be summarized as follows :— 
(1) That the upraised reef masses, whether atoll, barrier, or fringing 
reef, were formed in a region of elevation; (2) that such upraised 
reefs are of moderate thickness, their vertical measurement not 
usually exceeding the usual limit of the depth of the reef-coral 
zone ; (3) that these upraised reef masses in the majority of islands 
rest on a partially consolidated deposit, which possesses the characters 
of the “ volcanic muds” that were found during the “Challenger ” 
expedition to be forming round volcanic islands; (4), that this 
deposit envelopes anciently submerged volcanic peaks. 
Plans and sections are given in the two accompanying plates, and, 
if these are to be relied upon, the coral limestones are shown to exist 
